My name is Shinya Ogata and I work in the Environmental Section at PTM. I mainly work on computational flow dynamics, which involves the use of software to simulate heat environments.
Cooling system temperature settings
Recently there are an increasing number of offices increasing the temperature setting on their cooling systems. By increasing the temperature setting we can certainly save energy however, people are likely to start feeling the heat? One obvious answer is to use a desk fan. You soon feel cooler when a fan is blowing directly at you, but how comfortable is it?
“PMV” – an indicator of comfort
PMV, short for Predicted Mean Vote, is an index that is widely used in architecture to indicate levels of comfort. A prediction of the level of comfort is made based on data collected from experiments carried out on 1000 subjects. The index has 7 levels from -3 (very cold) to +3 (very hot), and the closer to zero the indicator is, the more comfortable it is. To work out the PMV for a certain space, 6 different conditions need to be determined: temperature, relative humidity, wind speed, mean radiant temperature, metabolic rate and amount of clothing.
PMV, short for Predicted Mean Vote, is an index that is widely used in architecture to indicate levels of comfort. A prediction of the level of comfort is made based on data collected from experiments carried out on 1000 subjects. The index has 7 levels from -3 (very cold) to +3 (very hot), and the closer to zero the indicator is, the more comfortable it is. To work out the PMV for a certain space, 6 different conditions need to be determined: temperature, relative humidity, wind speed, mean radiant temperature, metabolic rate and amount of clothing.
Cooling system temperature settings & comfort
Let’s compare comfort levels at different temperature settings of 26°C & 28°C. The graph below shows the relationship between air temperature, air speed, and PMV. Point 1) shows the setting at 26°C with no fan, while point 2) shows the setting at 28°C with a fan. When the fan is used, the air speed is about 0.6m/s. Look at the PMV in each case, the value for point 1) is between 0 to 1, while that for point 2) is very close to 0 which indicates the most comfortable environment.
Let’s compare comfort levels at different temperature settings of 26°C & 28°C. The graph below shows the relationship between air temperature, air speed, and PMV. Point 1) shows the setting at 26°C with no fan, while point 2) shows the setting at 28°C with a fan. When the fan is used, the air speed is about 0.6m/s. Look at the PMV in each case, the value for point 1) is between 0 to 1, while that for point 2) is very close to 0 which indicates the most comfortable environment.
Therefore, when a fan is used and the air speed is about 0.6m/s and blowing directly at you, whether the setting is at 26°C or 28°C, you can achieve comparable levels of comfort.
Energy saving and discomfort
There is the idea that energy saving is something that creates discomfort and is something to be endured however, as I explained above, with a little ingenuity improvements in both energy saving and comfort are possible. Here, I’ve used the use of fans as an example however, there are many other possibilities that could be devised. There’s no reason why we can’t all work towards creating comfortable environments and saving energy!
Shinya Ogata
Environmental GroupVisit our website at http://www.ptmtokyo.co.jp/
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